Hanatoxin modifies the gating of a voltage-dependent K+ channel through multiple binding sites

We studied the mechanism by which Hanatoxin (HaTx) inhibits the drk1 voltage-gated K+ channel. HaTx inhibits the K+ channel by shifting channel opening to more depolarized voltages. Channels opened by strong depolarization in the presence of HaTx deactivate much faster upon repolarization, indicating that toxin bound channels can open. Thus, HaTx inhibits the drk1 K+ channel, not by physically occluding the ion conduction pore, but by modifying channel gating. Occupancy of the channel by HaTx was studied using various strength depolarizations. The concentration dependence for equilibrium occupancy as well as the kinetics of onset and recovery from inhibition indicate that multiple HaTx molecules can simultaneously bind to a single K+ channel. These results are consistent with a simple model in which HaTx binds to the surface of the drk1 K+ channel at four equivalent sites and alters the energetics of channel gating.